Model Engineering	An Indexing Quick-Change Toolpost
	Introduction	Description	Construction	Toolholders

	Here is a selection of parts on which all the turning has been done, but nothing else. I worked in this order to minimise the number of change-overs from turning to milling. I roughed out the body, and then finished all the other parts before taking the body any futher. (The full size picture is nearly 1Mbyte.)
	This view shows the main assemblies that fit into the toolpost body. On the left is the post assembly. Working from the bottom there is: the post itself; the hardened index plate; the retaining nut; the clamping collet; and the clamp lever assembly, which is Loctited together and consists of the tapered nut, the large ball & handle, and the small ball. The angular position of the index plate is fixed by a dowel into the top slide. The collet arrangement did not result in the accurate repeatability intended, and I am trying out a different arrangement. The index assembly is in the centre. Again, working up, we have: the hardened index pin; the plunger, made from a cap-head bolt; the engaging spring; the face cam; the locking sleeve; the cap; and again a ball handle assembly in which the small ball is made separately. The cam follower is a hardened pin which passes diametrically through the plunger. When the index pin is flipped into engagement, the firm but gentle 'per-clack' is most satisfying. The arrangement at the bottom is the toolholder clamp. From the right, there is: the clamp screw assembly which has the large ball as its head for strength, with the handle shank and small ball as separate pieces Loctited on; a hardened thrust washer; the bearing sleeve, with a bronze bush inside; the retaining nut; the bronze adjusting nut, which is 5/8" x 26 TPI outside, and 7/6" Whit. inside; the locking ring; and finally, the dovetail clamp, which is internally threaded and provided with a keyway to limit rotation.
	The face cam was one of the trickiest parts to make. It is symetrical to eliminate side loads. There is a ledge at the top of the slope to hold the plunger in the disengaged position. The cam was mounted on the dividing head and step milled with a 3/32" cutter (in the drill chuck for clearance). The discolouration is due to Aga-tempering it for too long. The spring is home wound.